Optical filtering is an important concept in optics, and is commonly involved in a variety of optical components and instruments. One example is to use optical filters for a flat panel display. A flat panel display uses a light source, a tunable optical switch and a color filter. Liquid crystal is typically used to modulate the intensity of the light through a pixel. However, the response time of liquid crystal is much slower than that of a typical electronics circuit. And color filters are also used to select a specific spectral range for the pixel. Because of the spectral broadness and spectral irregular shape of the filter, the color quality is hard to control. Therefore it would be much more useful to have a material or a device that selectively transmits light only in a narrow range of frequencies within a broad spectrum and dynamically with a faster control mechanism.
Filters made from wire-mesh or metallic grids have been used extensively for filtering light in the far IR (infrared) spectrum. Such filters and devices incorporating the filters are disclosed in U.S. application Ser. Nos. 10/566,946 (now U.S. Pat. No. 7,456,383) and 11/345,673 (now U.S. Pat. No. 7,420,156) filed on Jul. 22, 2004 and Feb. 2, 2006, respectively, both of which are incorporated herein by reference in their entirety. These filters comprise thin metallic wires (much thinner than the wavelengths to be transmitted) deposited on an optically transparent substrate. The filters are characterized by a transmission spectrum having a peak at approximately 1.2 times the periodicity of the mesh. The peak is very broad and fixed, typically greater than half of the periodicity of the mesh. These filters would be much more useful if their transmission spectra could be modulated fast and narrowed to make them more selective.